A step regulating device for transformers is known from DE 913 933 and has a motor drive that drives a load switch and two tap selectors. Whereas one of the tap selectors preselects the uneven-numbered taps of the transformer, the other is responsible for preselection of the even-numbered taps. The actual switching over under load is carried out by the load switch. Each of the tap selectors has a slide that runs along a guide and that is driven by a traction element that runs over deflecting rollers, via an entraining formation seated at this element. Each slide carries switch contacts by which an electrically conductive connection between a contact rail and the taps of the transformer can be produced.
The individual selectors are actuated in alternation and the taps of the transformer changed by a discontinuous transmission. On reaching a specific tap, the roller of a lever that is attached to the transmission element, engages in the groove of a disk that is connected with the reverser, and thus actuates this.
A disadvantage of the existing step regulating device is the use of two individual selectors. These not only require a large amount of constructional space, but also impose high demands on the connection with the discontinuous transmission. The two selectors each need an individual guide, an individual slide and an individual traction element inclusive of bearings. Moreover, the coupling of the reverser to the selector as well as the actuation thereof is complex and susceptible to fault. The solution realized here by a lever with rollers—that in addition is at only one traction element—represents a high level of maintenance effort due to the numerous movable parts. Many errors can arise already during assembly in the case of numerous individual parts of that kind.